John and Lorraine become friends with the Pigman - real name Mr Pignati - in a rather unusual way, by playing a trick on him.
Bored and dissatisfied with their lives, John and Lorraine, along with two other friends take to making prank phone calls to random people picked from the phone book. It is Lorraine who turns up Mr Pignati's number, and calls him pretending to be from a charity and asking for a donation. He sounds so pleasant and friendly on the phone that Lorraine feels ashamed of gulling him, but John takes the game a step further by arranging to call at his house to collect his donation.
When John and Lorraine go to his house, the friendly impression he made over the phone is fully reinforced.
When Angelo Pignati came to the door, I wish you could have seen him. He was in his late 50s and was pretty big, and he had a bit of a beer stomach. But the part that slaughtered me was this great big smile on his face. He looked so glad to see us I thought his eyes were going to twinkle out of his head. (chapter 5)
John here admits to being quite overwhelmed by the sheer affability of the man. He is such a cheerful, obliging person that John and Lorraine simply can't help taking to him, and they all become good friends. In fact they start visiting him regularly. What started out as a mischievous prank on their part unexpectedly leads to an unlikely friendship between a lonely middle-aged man and two disaffected teenagers.
However, this friendship also leads to tragedy. John and Lorraine unintentionally become friends with Mr Pignati; they also most inadvertently help to precipitate his death. He gives them the run of his house, but on one occasion they have a party there where the guests get out of hand and end up trashing the place. This causes Mr Pignati to have a heart attack, and shortly afterwards he succumbs to another. John and Lorraine are left feeling very guilty over their role – however unintentional - in his death. So their friendship with Mr Pignati ends up having enormous consequences for all three of them, which none could have predicted.